1. Field of the Invention
Aspects of the present invention relate to a coupling apparatus that performs a coupling function in cooperation with a rotation of a knob and an image forming apparatus employing the same and, more particularly, to a coupling apparatus installed in a small space to be automatically decoupled when a force applied to a knob is released and an image forming apparatus employing the same.
2. Related Art
Generally, an image forming apparatus driven by a motor is provided with a coupling apparatus between a power supply unit and a driving unit so that power can be automatically discontinued when a cover is opened while the power is on. FIGS. 1A and 1B are schematic views illustrating a coupling apparatus for a conventional image forming apparatus. In the coupling apparatus for a conventional image forming apparatus, a driving gear 25 and a driving power transmitting gear 35 are mutually engaged or disengaged in cooperation with an opening and closing operation of a front cover (not shown) of an image forming apparatus. The driving gear 25 is provided on a shaft 27 of a driving roller (not shown) that rotatably drives a transfer belt (not shown) to be driven lengthwise of the shaft 27 by an operation of a coupling lever 21 to be described later.
In order to perform the above-described coupling function, the conventional coupling apparatus includes a locking lever 15 rotatably provided in a frame 10, a coupling lever 21 rotated in cooperation with the locking lever 15, and a tensile spring 17 provided between the frame 10 and the locking lever 15. The locking lever 15 is rotated by an opening and closing operation of the front cover. If the front cover is closed, the locking lever 15 rotates from a position shown in FIG. 1A to a position shown in FIG. 1B. The tensile spring 17 pulls the locking lever 15 so as to locate the locking lever 15 in the position shown in FIG. 1A while the front cover is open. When the locking lever 15 rotates, the tensile spring 17 pulls the locking lever 15 to a direction to accelerate the rotation of the locking lever 15 at the moment when the rotating angle exceeds an elastic bias critical point. The locking lever 15 snaps to the position shown in FIG. 1B by the elastic force.
The coupling lever 21 is rotatably installed and centered around on the shaft 27 of the driving roller (not shown). The coupling level 21 rotates in cooperation with the rotation of the locking lever 15. A long hole 21a is formed in the coupling lever 21, and a guide projection 15a coupled to the long hole 21a is formed in the locking lever 15. When the locking lever 15 rotates, the guide projection 15a slides along the long hole 21a and guides the rotation of the coupling lever 21.
However, the coupling apparatus according to the above described configuration has several problems. First, an error by the user or an external impact while the front cover is open may cause the position of a driving gear and a power transmitting gear to change to the position shown in FIG. 1B (where the driving and power transmitting gears 25 and 35 are engaged with each other) by rotation of the locking lever 15 and an elastic force of the tensile spring. As such, the coupling structure may be damaged. If the user wants to close the front cover while in a coupled state by the snap operation of the locking lever 15, the front cover is not closed normally, and the front cover or the coupling structure may be damaged by an abnormal contact between the front cover and the coupling apparatus.
Second, since the locking lever 15 and the coupling lever 21 have a different center of rotation, the configuration can be complicated and takes up a large amount of space. Third, since the locking lever 15 and the coupling lever 21 are engaged in a sliding system, durability of the system is reduced. Since the front cover of the image forming apparatus is repeatedly opened and closed, and accordingly, a strong coupling structure is related to a color registration quality of the image forming apparatus, the sliding system wears out quickly and will need to be replaced often.